Hot stepwise drawing with independent free-wheeling idler rolls

ABSTRACT

By using at least three independent, free-wheeling idler rolls, high speed hot drawing of orientable synthetic strand material such as polybenzimidazole yarn is accomplished in a more favorable and improved manner as stepwise drawing is permitted in each of the passes through the heating zone; the strand material being drawn wherever the yield point occurs, rather than at a predetermined location for a fixed amount which might not be optimum.

[4 1 Jan. 15, 1974 limited States Patent [191 Bohr-er et al.

C t a MSNSHSB 3793490 5556667 9999999 mmmwwlt w 4335006 3638845 473 4 2 2088440 ,3 1, 3, 2223333 [73] Assignee: Celanese Corporation, New York, Primary Examiner-Louis K. Rimrodt N.Y. AttorneyeThomas J. Morgan et al.

[22] Filed: Nov. 10, 1970 ABSTRACT 211 Appl.No.:88,461

Related US. Application Data Continuation-in-part of Ser. No. 769,893, Oct. 23, 1968, abandoned.

syn-

etic strand material such as polybenzimidazole yarn is accomplished in a more favorable and improved manner as stepwise drawing is permitted in each of the By using at least three independent, free-wheelin idler rolls, high speed hot drawing of orientable th passes through the heating zone; the strand material being drawn wherever the yield point occurs, rather than at a predetermined location for a fixed amount which might not be optimum.

32 O In 9 712 837,0 2 D1 s 6 mm fi u" 4 "Hm/O "n82 WW "u" d e t n i m m n C am 5 e "u" c "U" n e mmm a Tm m m m r R U d td Ul F HUN N 555 5 UNITED STATES PATENTS 2,398,975 Swanson...........,.................. 28/7l.3 5 Claims, 3 Drawing Figures 1 HOT STEPWISE DRAWING WITH INDEPENDENT FREE-WHEELING IDLER ROLLS This is a continuation-in-part of application Ser. No. 769,893, filed Oct. 23, 1968 now abandoned.

BACKGROUND OF THE INVENTION order to obtain the necessary orientation and improve physical properties such as tensile strength.

This is usually done by feeding the strand material from a supply package to feed and draw rolls in series, the draw rolls having a greater peripheral speed than the feed rolls. The strand material is heated between the feed and draw rolls by passing it, for example, through a zone of radiant vapors.

Further, to achieve the desired residence time in the heating zone; to ensure adequate improvement in tensile properties, and at the same time to minimize necessary work space, the strand material is normally passed back and forth through the heating zone a number of times about a pair of idler rolls, spaced across at least a portion of the heating zone, at opposite ends of the zone to function as guide and return members.

The conventional idler roll is a one-piece cylindrical or frustoconical roll or roller having one or more grooves formed about its circumference for guiding a corresponding number of strand portions. Whenever such a one piece idler roll is rotated the grooves travel, of course, at uniform, fixed ratio, peripheral speeds.

FIG. ll can be used to illustrate a conventional drawing system by envisioning units 6 and 7 each to be a one piece idler roll, i.e., together they comprise a single idler roll pair. Strand material 1 from a supply bobbin 2 is wound around a feed roll 3 and its idler spacer a sufficient number of times to ensure against slippage and is conducted through a centering guide 4 and through the front of a heating zone 5. The strand exiting from the rear end of the heating zone makes a onehalf wrap around the single-piece idler roll 6 and is then conducted back through the heating zone for a second pass.

Again, upon emerging at the front, the strand makes a one-half wrap around the other single-piece idler roll 7 and is again conducted back through the heating zone for a third pass.

In this manner, wraps are additionally added to this idler pair to bring the strand material up to a given temperature; to heat set the strand material; etc. Upon exiting from the furnace on the last pass, the strand goes through a centering guide 8 to draw roll 10 with its spacer idler and is then taken up onto a bobbin 11. Draw roll 10 is normally rotated at a higher peripheral speed than feed roll 3 in order to draw or stretch the heated strand material.

Assuming no slippage, the single-piece, heating zone idler rolls must of necessity rotate at the same peripheral speed and therefore strand drawing of any substantial magnitude can only be accomplished during the initial entry and final exiting passes through the heating zone.

Further, even whenusing a pair of frusto-conical idler rolls, drawing is limited to a fixed amount at fixed locations during passes other than the initial and final passes through the heating zone.

Moreover, as drawing speed is increased, a reduced retention time in the heating zone for the initial pass can result in the strand material not reaching the temperature necessary for drawing. This will shift substantially all of the drawing to the final pass through the heating zone as is illustrated in Example 1.

Thus, due tocertain minimum residence time requirements as well as minimum draw requirements, drawing speed or productivity is particularly limited when using the above described pair of one-piece idlers in systems needing four or more passes of the strand material through the heating zone.

The above limitations and disadvantages of utilizing the conventional system of a pair of idler rolls are particularly apparent when high temperature resistant filaments or fibers are being drawn. For example, when certain polybenzimidazole fibers and particularly certain aromatic polybenzimidazole fibers are subjected to hot drawing operations where drawing conditions are not within certain critical ranges, the fibers foam and- /or explode, resulting in a porous fiber product having relatively low tensile properties.

SUMMARY OF THE INVENTION Accordingly, a primary object of the present invention is to increase production capabilities in systems for hot drawing orientable synthetic strand material.

Another object of the present invention is to improve physical properties of orientable synthetic strand material while achieving high drawing speeds.

Another object of the present invention is to increase maximum draw ratios while achieving improved stability of drawn material.

Other and further objects and advantages of the present invention will become apparent from the following more detailed description.

In accordance with the present invention, hot drawing of orientable synthetic strand material such as polybenzimidazole yarn is accomplished in a more favorable and improved manner as stepwise drawing is permitted in each of the passes through the heating zone, the strand material being drawn wherever the yield point occurs, rather than at a predetermined location for a fixed amount which might not be optimum. This is achieved by using at least three independent, freewheeling heating zone idler rolls.

In one aspect of the invention, processes wherein orientable synthetic strand material is hot drawn by passing strand material in tension through a heating zone, and about a pair of rotatable guide-and-return members to effect at least four passages of strand material through the zone, are improved by passing the strand material about at least three independent, freewheeling rotatable guide-and-return members to allow strand drawing wherever the yield point occurs.

In another aspect of the invention, apparatus is provided for hot drawing strand material which apparatus comprises strand supply means, strand take-up means, and first and second idler roll means for permitting simultaneously at least four passages of the strand material through the heating zone, said first and second idler roll means adapted to be spaced across at least a portion of the heating zone, at least one of said idler roll means comprising at least two independent freewheeling idler rolls, whereby strand drawing is allowed wherever the yield point occurs.

Other and further aspects of the present invention will become apparent from the following more detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a preferred form of the apparatus for carrying out the present invention;

FIG. 2 is a more detailed view of independent, freewheeling idler rolls; and

FIG. 3 illustrates yet another embodiment of the invention wherein the heating zone comprises a heated drawing shoe or plate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates the present invention in a preferred embodiment. Strand material 1 from a supply bobbin 2 is wound around a feed roll and spacer idler roll 3 a sufficient number of times to ensure against slippage and is conducted through a centering guide 4 and through a muffle furnace 5. The strand exiting from the furnace makes a one-half wrap around an independent free-wheeling grooved idler roll 6a and is then conducted back through the furnace for a second pass.

Again, upon emerging at the front of the furnace, the strand makes one-half wrap around an independent free-wheeling grooved idler roll 7a and is again conducted back through the furnace for a third pass. The strand exiting from the third pass makes a one-half wrap around on independent free-wheeling grooved idler roll 6b and is then conducted back through the furnace for a fourth pass. In this manner, at least four, preferably five or more, and as many as fifty or more passes may advantageously be made in accordance with the present invention. Upon exiting from the furnace on the last pass, the strand goes through a centering guide 8 to draw roll 10 and its spacer idler and is then taken up onto a bobbin 11. Draw roll 10 is rotated at a higher peripheral speed than feed roll 3 in order to draw or stretch the heated strand material.

FIG. 2 shows in more detail exemplary idler roll means in accordance with the present invention, which means comprise a plurality of independent freewheeling grooved idler rolls A through F mounted on a common supporting shaft 12 and adapted to rotate freely, i.e., not being power-driven; and independently of one another, i.e., not being geared or otherwise rigidly connected to each other.

FIG. 3 shows another embodiment of the present invention similar to that shown in FIG. 1 except the means for supplying and maintaining a heating zone comprises a heated shoe 13. The strand material may also be heated by passing it over a heated pin or through heated liquids or vapors (not shown).

To be noted is that the idlers need not be closely spaced, for the actual stretching is believed to occur between successive idlers not on them, i.e., the stepwise drawing takes place in the heating zone between each consecutive idler from the slowest accepting yarn from the supply roll to the fastest which feeds the stretch roll. Each idler need only be of sufficient width to serve as a guide track for the yarn or fiber to be drawn and of course may possess a groove.

Moreover, means (not shown) for measuring and controlling the temperatures of the muffle furnace and the heated shoe shown in the drawings can also be utilized in the practice of the present invention.

Strand material which may be treated in accordance with the present invention includes filaments and yarns of fiber-forming polymers such as, for example, the polybenzimidazoles, e.g., poly-2-2-m-phenylene- 5,5- bibenzimidazole; the polyesters, e.g., polyethylene terephthalate; the polyolefins, e.g., polypropylene; the polyamides, e.g., polyhexamethylene adipamide; and the acrylics, e.g., polyacrylonitrile.

Using the above-mentioned polymers, filaments and yarns having a denier range, for example, of about 10 to 2,000, and preferably about 50 to 500, may be treated in accordance with the present invention.

Drawing of the above-mentioned strand material can be accomplished with the apparatus illustrated in FIG. 1 by rotating the feed roll 3 at a rate R, and rotating the draw roll 10 at a rate R The resulting overall draw ratio is R /R For example, polybenzimidazole fibers may be drawn at any desired draw ratio below that at which the fiber breaks, typically in the range of about 1.5:1 to 3.5: l and preferably from about 2.0:1 to 3.2: I.

To achieve the desired improvement in physical properties, the strand material must have a sufficient residence time in the heating zone.

In general, residence time depends upon the strand material being treated and the temperatures in the heating zone.

For example, residence times of about 0.001 to 60 seconds may in general be adequate for the strand material described above. More specifically, residence times of about 5 to 20 seconds are normally sufficient for filaments and fibers of polybenzimidazole. Of course, larger yarns will generally require a longer residence time than smaller yarns.

The temperatures maintained in the heating zone should be high enough to allow the desired drawing and orientation of the strand material, but below that necessary to cause any significant degradation of the strand material. For example, temperatures in the range of about 300 to 700C., and preferably about 400 to 600C., would normally be adequate for polybenzimidazole filaments and fibers.

As stated, a significant advantage of the present invention is the capability of achieving high drawing speeds while attaining improved physical properties of the strand material. For example, drawing speed measured at the feed roll in the range of about to 300 m/min., or even higher, may be obtained without difficulty.

EXAMPLE I The stretching phenomena in a conventional hot drawing system was studied using a single one-piece free-wheeling idler roll at each end of a four foot muffle furnace to allow multiple yarn passes through the furnace, i.e., the yarn path went from a slowly driven feed roll; to multiple wraps around a single pair of freewheeling idler rolls; to a faster driven stretch roll: the multiple wraps traveling through a 500C. muffle furnace located between the idler rolls.

The strand material utilized was 12 dpf poly-2,2'-(mphenylene)-5-5'-bibenzimidazole yarn. The polymer Speed, m/min. Draw ratios No. of passes Supply Stretch Idlers Totnl First Second 7 40 64 55.7 1.6 1.39 1.15 7 40 80 68.0 2.0 1.70 1.18 7 40 96 80.5 2.4 2.01 1.19 11 70 112 85 1.6 1.21 1.32 11 70 140 99 2.0 1.41 l 42 ll 70 168 96 2.4 1.37

*Total Amie 5 1 1 draw ratio) (2nd draw ratio).

The results show that two-stage drawing was occuring in the furnace, i.e., in the first pass in the furnace between the supply an idler roll and in the last pass between the other idler roll and the stretch roll. When the drawing speed is low, the major part of the total drawing is done at the first stage, with a small portion of the drawing accomplished at the second stage. However, when the drawing speed is increased, this situation was reversed. In addition, the ratio between the amounts of second and first stage drawing increases with increasing total draw ratio.

EXAMPLE II A hot drawing system was examined as in Example I utilizing three independent, free-wheeling idler rolls; two positioned at the entrance to the muffle furnace and one at the exit. The yarn from the supply roll passed through the furnace; made one-half wrap around the exit idler roll; passed back through the furnace and made one-half wrap around the Nofl entrance idler. Five successive wraps were then made between these two idlers. On the fifth wrap around the exit idler, the yarn passed back through the furnace; made a one-half wrap around entrance idler No. 2; passed back through the furnace to the stretch roll and take-up. The results are as follows:

No. of Speed, m/min.

Passes Supply Idlers Stretch Exit Entrance l Entrance 2 DRAW RATIOS Total Exit/Sp. No. 2/Exit St/No. 2

EXAMPLE 111 Temp. C.

Supply Total Prespeed draw No. of TEN Elong. MOD heater Furnace (ml min) ratio passes (g/d) TE I (g/d) EXAMPLE IV Utilizing the three-idler system of Example 11 with the FBI yarn of Example I a significant improvement in the product physical properties was realized even without the use of the preheater oven.

Supply Total Furnace speed draw No. of TEN Elong. MOD temp. C.) (m/min) ratio passes (gld) TE" (g/d) However, the properties began to drop as the input speed increased, as the above data shows.

EXAMPLE V The following example illustrates the preferred stepwise drawing manner in which the improved tensile properties with higher drawing speeds were obtained I by the instant invention. The strand material is that of Example I. The apparatus used corresponds to that shown in FIG. 1, i.e., one independent free-wheeling idler roll per wrap as the yarn passes back and forth through the furnace, and the particular process conditions and properties obtained are given below. The muffle furnace used was four feet long as measured from the strand entrance to the strand exit.

Total As can be seen from above, it is possible by the present invention to quadruple the drawing speed from 50 m/min to 200 m/min and produce polybenzimidazole yarns having improved physical properties, e.g., tenacity values of five to six grams per denier or more and tensile factors (TE in excess of 25. The-significance of the tensile factor TE is more fully discussed in an article by Dr. Arnold J. Rosenthal, TE, An lndex for Relating Fiber Tenacity and Elongation, Proceedings of the Symposium on Polypropylene Fibers, September, 1964, A Southern Research Institute Publication, Birmingham, Ala.

Similar improvement in drawing speeds and physical properties may be achieved with filaments and fibers of other aromatic polybenzimidazoles such as poly- 2,2'(m-phenylene) 5,5'- bibenzimidazole; poly-2,2- (pyridylene-3",5")-5,5'-bibenzimida-zole; poly-2,2- (furylene-2' ',5 )-5 ,5 '-bibenzimidazole;poly-2,2 (naphthalene-l,6")-5,5-bibenzimidazole; poly2,2'- (biphenylene 4",4")-5,5'-bibenzimidazole; poly-2,2- amylene-5,5'-bibenzimidazole; poly-2,2'-octamethylene-5,5'-bibenzimidazole; poly 2,6-(m-phenylene)- diimidazobenzene; poly-2,2'-cyclohexenyl-5 ,5 bibenzimidazole; poly-2,2 m-phenylene )-5 ,5 di( benzimidazole) ether; poly-2,2 m-phenylene 5 ,5 '-di( benzimidazole) sulfide; poly-2 ,2 mphenylene)-5,5'-di(benzimidazole)sulfone; poly-2,2 (m-phenylene)-5,5'-di(benzimidazole)methane; poly- 2',2"(m-phenylene) di(benzimidazole)propane-2,2; poly-2',2(m-phenylene)- 5,5" di(benzimidazole)ethylene-l,2; as well as the other aforementioned synthetic strand materials.

The principle, preferred embodiments, and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein, however, may be practiced otherwise than is described without departing from the scope of the appended claims.

What is claimed is:

1. Apparatus for hot drawing orientable synthetic strand material, which apparatus comprises strand supply means, strand take-up means, and first and second idler roll means for permitting at least four simultaneous passages of the strand material through the heating zone, said first and second idler roll means adapted to be spaced across at least a portion of the heating zone, at least one of said idler roll means comprising at least two independent free-wheeling idler rolls, whereby strand drawing is allowed wherever the yield point occurs.

2. The apparatus of claim 1 wherein each of said first and second idler roll means comprises at least two independent, free-wheeling idler rolls, whereby at least five simultaneous passages of the strand material through the heating zone is permitted.

3. The apparatus of claim 2 wherein the heating zone is a zone of radiant heat, said zone being elongated in one direction, said first and second-idler roll means positioned at each of the two elongated ends of said zone to permit the multiple simultaneous passing of the strand material along the axis of elongation,

4. Apparatus for hot drawing orientable synthetic strand material, which apparatus comprises means for supplying and maintaining a zone of controlled heat, and means for permitting at least four simultaneous passages of strand material in tension through said zone comprising idler roll means having a plurality of independent, free-wheeling idler rolls mounted on a common supporting shaft, said idler roll means positioned at a strand entrance and at a strand exit to said zone, whereby strand drawing is allowed wherever the yield point occurs.

5. The apparatus of claim 4 wherein the means for placing the strand material in tension comprises strand supply means and strand take-up means, said strand take-up means adapted to rotate at a higher peripheral speed than said strand supply means to draw the heated strand material. 

1. Apparatus for hot drawing orientable synthetic strand material, which apparatus comprises strand supply means, strand take-up means, and first and second idler roll means for permitting at least four simultaneous passages of the strand material through the heating zone, said first and second idler roll means adapted to be spaced across at least a portion of the heating zone, at least one of said idler roll means comprising at least two independent free-wheeling idler rolls, whereby strand drawing is allowed wherever the yield point occurs.
 2. The apparatus of claim 1 wherein each of said first and second idler roll means comprises at least two independent, free-wheeling idler rolls, whereby at least five simultaneous passages of the strand material through the heating zone is permitted.
 3. The apparatus of claim 2 wherein the heating zone is a zone of radiant heat, said zone being elongated in one direction, said first and second idler roll means positioned at each of the two elongated ends of said zone to permit the multiple simultaneous passing of the strand material along the axis of elongation.
 4. Apparatus for hot drawing orientable synthetic strand material, which apparatus comprises means for supplying and maintaining a zone of controlled heat, and means for permitting at least four simultaneous passages of strand material in tension through said zone comprising idler roll means having a plurality of independent, free-wheeling idler rolls mounted on a common supporting shaft, said idler roll means positioned at a strand entrance and at a strand exit to said zone, whereby strand drawing is allowed wherever the yield point occurs.
 5. The apparatus of claim 4 wherein the means for placing the strand material in tension comprises strand supply means and strand take-up means, said strand take-up means adapted to rotate at a higher peripheral speed than said strand supply means to draw the heated strand material. 